Video multicast over IEEE 802.11 wireless local area networks (WLANs) enables the distribution of live or pre-recorded video to multiple receivers efficiently, for example, the distribution of TV programs or location specific video information in hotspots such as airport, café, hotel and shopping mall, etc. Users can watch their favorite TV programs on mobile devices while browsing the Internet. Other examples include extension of satellite TV services to mobile devices in tunnels and subways using WLANs, wireless video classes and video training for enterprise users, etc.
The error rate is usually high in wireless networks. For multicast, the IEEE 802.11 wireless link layer does not perform retransmission of lost packets. The data frames are discarded at the receiver in the event of an error. The required reliability cannot, therefore, be guaranteed to the users without excellent receiving conditions. Furthermore, in a video multicast application, the receivers for the same video may experience different channel conditions and the channel condition for a receiver varies at different times due to fading, shadowing, interference and mobility. New receivers may join during the session or some receivers may leave resulting in a changed user topology.
It is known in the art, that to achieve reliable video transmission in wireless local area networks (WLANs), each network protocol layer provides an individual solution, for example, selection of appropriate physical layer modulation and channel coding (PHY mode), media access control (MAC) layer retransmission, application layer forward error correction (FEC), packet size optimization, usage of scalable video coding, etc. However, the mechanisms at each layer operate independently and their parameters are chosen independently. This layered approach does not yield an optimal system performance for video delivery.
Recently, cross-layer design to achieve optimal system performance for video transport in WLANs has attracted some attentions. A cross-layer protection strategy for video unicast in WLANs was proposed by jointly adapting MAC retransmission limit, application layer FEC, packetization and scalable video coding. This strategy is, however, not applicable to multicast. First, for multicast, multiple users receive the same video and the overall video quality of all the users must be considered for optimizing system design. It should be noted that the receivers of the same video may experience different channel conditions at the same time and the same receiver may also experience different channel conditions at different times. Receivers may join or leave during the session so that the receiver topology changes dynamically. Adaptation decisions cannot be made based on a single user's feedback as in the prior art. Second, the IEEE 802.11 link layer does not perform retransmission of lost multicast data frames. The frames are discarded at the receiving MAC in the event of errors. Third, in the prior art, the PHY mode was fixed. The PHY mode is an important parameter impacting the video transmission quality, especially in the case of multicast (no per user link adaptation and retransmission) and the PHY mode, thus, needs to be taken into account for cross-layer optimization. Fourth, in the prior art the bandwidth allocation is optimized. It is not straightforward to optimize the bandwidth allocation when the channel bandwidth is adjustable for different PHY modes. Instead the channel usage needs to be viewed as a more general resource.
The problem to be solved in this invention is how to provide quality of services for all the users of the same multicast video in the desired/target service area while efficiently utilizing available wireless network resources. Therefore, new cross layer optimization algorithms are necessary to provide efficient and robust video multicast services over IEEE 802.11 WLANs in order to provide quality of services for all the users of the same multicast video in the desired/target service area while efficiently utilizing available wireless network resources.